Patent Application
20100065436
The present invention relates to a method of extracting precious metals from waste catalysts through an electrochemical process.
Platinum group metals (PGMs) including Pt and Pd have unique chemical characteristics, such as catalytic reduction, as well as a high fusion point and an excellent resistance to chemical corrosion. The world average annual productivity of the platinum group metals is about 200 tons, in which more than 90% of the metals are produced in South Africa and the former Soviet Union, about 6% thereof are produced in Canada, and the remainders are produced in U.S.A., Australia, Japan and so forth. The platinum group metals are utilized as catalysts for automobiles and petrochemical industries, except for catalysts for electrical and electronics industries such as platinum group metal circuits.
Performances of the catalysts and components thereof deteriorate with the lapse of time. When their lifespan is terminated, they finally come into disuse. In particular, since the platinum group metals are expensive and the whole quantity thereof is imported, the recovery and recycling of the waste catalysts is economically beneficial, and plays an important role in effective use of resources.
Although several methods have been proposed in the recovery of the precious metals contained in carriers of the catalysts, they have their own technical advantages and disadvantages. In particular, since an ionization electric potential of the platinum group metals is very high, dissolution of the metal itself is difficult. It is further difficult to extract and separate the platinum group metals due to the catalyst carriers, other catalyst components, and pollution.
In general, a precious metal content of the waste catalyst is about 0.02% to about 5.0%. A method of extracting platinum (Pt), palladium (Pb), rhodium (Rh), and an alloy thereof from the waste catalysts by crushing the waste catalysts and electrolyzing the crushed catalysts contained in an electrolytic cell filled with an electrolyte and having an anion-exchange membrane has been disclosed. However, the anion-exchange membrane is very expensive, and since the lifespan of the membrane is shortened due to sedimentation of chlorine occurring in the extracting process, it should be frequently replaced. Also, since concentration of the precious metals in the extracted liquid is low, the separation of the precious metals is complicated, and the process cost is increased with the extracting time prolonged. In addition, the process should include many processing steps.
A solution of hydrochloric acid (HCl) with 5 to 35% concentration is generally used as the electrolyte. Leaching is carried out in a stationary filtering layer of the waste catalyst particles, or is carried out in a fluidal layer when the electrolyte is circulated through a leaching material layer. After that, the precious metals are surrounded by the solution reduced by carbon particles in a cathodic chamber of a second electrolytic cell having a cation-exchange membrane. Finally, the precious metals are again deposited in the fluidal layer by the electrolytic solution.
The current method of extracting the platinum group metals from inorganic substances such as the waste catalysts, slime, concentrates, and so forth, is carried out by simultaneously leaching the platinum group metals and precipitating the platinum group metal in a charged cathode. The method has some drawbacks in that it can obtain limited concentration in a filtering solution, and the process is complicated since it utilizes technological blocks separately positioned.
Therefore, the present invention has been made in view of the above-mentioned problems.
An object of the present invention is to provide a method of extracting platinum group metals from waste catalysts through an electrochemical process, which increases the productivity simply and economically.
In order to achieve the above and other objects, there is provided a method of extracting platinum group metals from waste catalysts through an electrochemical process, according to embodiments of the present invention, which comprises positioning the waste catalyst between both electrodes in an electrolyte, leaching the platinum group metals as regularly changing polarities of the electrodes to each other, and precipitating the platinum group metals on a cathode by circulating the electrolyte from an anode to a cathode.
In an embodiment of the present invention, the electrolyte includes a solution of hydrochloric acid with 0.3 to 10.0% concentration.
The electrochemical leaching is activated by multi-pole reverse electrodes in a state that the electrodes are transformed into multi-pole electrodes that can cause anodic dissolution of all metal materials.
The electrolyte is circulated from the anode to the cathode at a speed enough to prevent hydrated anionic chloride complexes of the precious metals from being drifted on the cathode.
According to the method of extracting platinum group metals from waste catalysts according to embodiments of the present invention, the platinum group metals can be extracted with a high efficiency and high yield. Also, the extracting process is simplified, thereby remarkably reducing costs required to extract the platinum group metals. In addition, the extraction of the platinum group metals from the waste catalysts is very useful to recycle the platinum group metals of which the whole quantity should be imported.
The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:
Reference will now be made in detail to the preferred embodiments of the present invention. It is to be understood that the following examples are illustrative only and the present invention is not limited thereto.
A method of extracting platinum group metals from waste catalysts through an electrochemical process according to the present invention may be utilized in the case of extracting platinum group metals from inorganic substances such as the waste catalysts, slime, concentrates, and so forth.
The crushed waste catalysts including 0.01 to 10.0%, preferably 0.1 to 5.0%, of precious metals may be interposed between a cathode and an anode in an electrolytic cell.
In an embodiment of the present invention, a solution of hydrochloric acid with 0.3 to 10.0% concentration is utilizes as an electrolyte.
The electrochemical leaching is activated by multi-pole reverse electrodes in a state that the electrodes are transformed into multi-pole electrodes that can cause anodic dissolution of metals in all materials.
There is no circulation of the electrolyte in the electrochemical leaching step. Initial activation of metals occurs on surfaces of particles of crushed waste catalysts under amorphous and connected conditions. The metal particles are transformed into dipoles in the waste catalysts under an external electric field to polarize the metal particles. The process of activation begins with dissolution of active centers of metal on the anode of each dipole. With the change of polarity, the dissolved metal is adhered to the surfaces of particles, which is accompanied by allocation of atomic hydrogen. The charge of each particle is increased in proportion to the quantity of besieged activated metals. The field induced between the anode and the cathode in the electrolyte cell is accordingly increased. A feedback occurs to allow particles to be carried away in a process of increasing passive metal. All particles are transformed into dipoles on electric wire particles under the external electric field to divide charges. Thus, the whole weight of a bulk material starts to represent volumetric multi-polar electrode which can cause anodic dissolution of metal in all volume of the material.
Such preliminary processing of the material activates the following electrochemical leaching of the precious metals on the basis of the anodic dissolution. If such activation process is not carried out, the electrochemical leaching occurs in the center of the respective particle, and thus the dissolution is quickly stopped. As a result, the most part of the precious metals remains on the carrier under the passive conditions, and a small amount of precious metals is positioned on the cathode.
On the anode: Cl−+2H2O−5e−→ClO2−5H+
Output of ClO2 depends on a degree of collateral reaction process which stores ions of chlorine (Cl−).
ClO2+5H+→Cl−+2H2O−5e−
In order to maintain the maximum output of ClO2, it is necessary to prevent ClO2 from coming in contact with the cathode until the precious metals are completely extracted from the waste catalysts.
On the cathode: 5H++5e−→5H
If atoms of hydrogen are formed, the atoms are discharged from the surface of the material thereby to destroy and activate the surface. Due to the electrodes with its polarity reversed, all particles are exposed to the anodic dissolution.
Pt0+e−→Pt+
That is, metal particles are drifted to the cathode electrolytic cell, and are transited in the electrolyte. Otherwise, the metal particles are directly transited in the electrolyte by go-ahead method or other method of ionic conductivity.
The electrolyte is circulated from the anode to the cathode at a speed that can prevent hydrated anionic chloride complexes of the precious metals from being on drifted on the cathode.
If the electrolyte having 0.3 to 10.0% of HCl is circulated, the precious metals are precipitated on the cathode in a direction opposite to drift of anionic complexes of the precious metals, i.e., from the anode to the cathode.
Such circulation of the electrolyte is carried by a pump. The circulation of the electrolyte is to activate the sedimentation of all metals in the electrolyte. It is noted to prevent the hydrated anionic chloride complexes of the precious metals, which is formed at the electrochemical leaching, from being drifted on the cathode, which is observed in the initial process by formation of brown smoke on the anode.
The dissolved metals (platinum or palladium-hydrochloride acids (hydrated anionic chloride complexes of the precious metals)) are drifted towards the anode. With the increased concentration of the anionic complexes on the anode, the brown smoke is gradually formed, and then is distributed towards the cathode. After that, the anionic complex is collapsed, and cations of the previous metals are drifted towards the cathode where the sedimentation is carried out.
In case of replacement by an external anolyte, rich metal is not generated on the cathode of metal. When the electrolyte is drifted from the cathode to the anode, the process of allocating the metal on the cathode ceases. Furthermore, the metals initially allocated on the cathode are dissolved. This means that high contents of chlorine which is in the anolyte dissolves the besieged metal.
In the circulation of the electrolyte from the anode to the cathode, the metals are intensively allocated on the cathode, and allocation speed of the metal is 2 to 5 times as fast as a static mode. This means that the anolyte is relatively increased as it is consumed for oxidization of the metal, and has rich active chlorine. When the electrolyte is quickly circulated, the formation of the brown smoke on the anode is stopped, and the allocation of the metal on the cathode is also stopped. In order to prevent the hydrated anionic chloride complexes of the precious metals which are formed at the leaching from being drifted toward the cathode, the electrolyte should be circulated from the anode to the cathode at a speed not to interrupt formation of the brown smoke on the anode. When concentration of the carrier is the highest value, the initial process can be visually observed.
Preferably, the current density at electrochemical sedimentation is 0.006 A/cm2 to 0.025 A/cm2. If the current density is up to 0.006 A/cm2/cm2, a sedimentation time is prolonged, while if the current density is above 0.025 A/cm2/cm2, hydrogen gas is generated.
40 liters of waste catalysts (palladium on granite) were filled between electrodes in an electrolytic cell having a size of 20×20×100 cm. Contents of palladium were 0.3 wt %, and were used as granular having a diameter of 5 mm without preliminary preparation. A solution of 2% HCl was used as the electrolyte, and was continuously circulated from an anode to a cathode at a speed of 0.5 liter/minute by using a pump. Temperature was maintained at 70° C.
Polarities of the electrodes were changed every 1 minute for 1 hour.
At the electrochemical sedimentation, 21V voltage and 6A current (current density: 0.015 A/cm2) were applied to the electrodes. Circulation speed of the electrolyte was determined not to interrupt formation of brown smoke on the cathode as the sedimentation was proceeding.
As a result, metal foils of metals including 85 to 90% of the precious metals were generated on the cathode. These metal foils were easily removed from the cathode.
Analyzing the results obtained after operating for 10 hours, concentration of palladium in the electrolyte was up to 1 ppm. Analyzing the waste catalyst after electrochemically extracting, contents of palladium were up to 0.0015%, and thus, 99.5% of palladium was extracted. Geometry of the waste catalysts was maintained intact, and a color was changed to white. No components of the waste catalysts were extracted, beside palladium. 1.25 kWh was consumed for electrolysis, and 7.5 kWh was consumed for heating and circulation of the electrolyte.
A method of extracting more palladium from an alumina-palladium catalyst which had been subjected to a leaching process was carried out. Contents of palladium were 0.02 to 0.03%, which was similar to those of palladium remaining on a carrier, disclosed in U.S. Pat. No. 4,775,452. A volume of the catalysts filled in an electrolytic cell was 40 liters, and the electrolytic cell was a cylinder having a diameter of 10 mm and a height of 15 mm. A solution of 0.03% HCl was used as an electrolyte, and a ratio of a solid phase and a liquid phase was set by 1:1. In order to activate surfaces of the catalysts, polarities of the electrodes were changed every 1 minute for 1 hour. The electrolyte was circulated to electrochemically extract the metals for 15 hours. Current density was 0.06 A/cm2. As a result, concentrate of palladium in a carrier was 0.005%, and concentration of palladium in the electrolyte was up to 1 ppm.
Alumina-palladium catalysts of 40 liters, of which a grain size was 3 to 5 mm, were filled in an electrolytic cell. A solution of 4% HCl was used as the electrolyte, and a ratio of a solid phase and a liquid phase was set by 1:1.
Polarities of the electrodes were changed every 1 minute for 1 hour so as to activate sedimentation. Current density was 0.025 A/cm2 (current of the electrolytic cell was 10 A), temperature was maintained at 70° C., and the electrolyte was circulated to electrochemically extract the metals for 20 hours, as Embodiment 1. As a result, 98% of platinum was extracted, and content of platinum adhered on the cathode as a granular conglomerate was 60 to 70%.
As can be seen from the foregoing, the extracting method of the present invention can extract the platinum group metals in high efficiency and high yield. Also, the extracting process is simplified, thereby remarkably reducing costs required to extract the platinum group metals. In addition, the extraction of the platinum group metals from the waste catalysts is very useful to recycle the platinum group metals which depend on importation for the full quantity. This invention is also applied to the extraction of other catalysts, for example Ni, Co and Mo, etc which is supported on the carriers.
While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment and the drawings. On the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1020060111811 | Nov 2006 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR2007/004828 | 10/2/2007 | WO | 00 | 5/11/2009 |
